The present invention relates to a hybrid drivetrain for a motor vehicle, having a first drive unit which has a first drive device by means of which first drive power can be provided, having a second drive unit which has a second drive device by means of which second drive power can be provided, having a drive output device which can be connected to driven wheels of the motor vehicle, having a first gearbox arrangement which has a first gearbox input and a first gearbox output, having a second gearbox arrangement which has a second gearbox input and a second gearbox output, wherein the first drive device is connected to the first gearbox input and wherein the second drive device is connected to the second gearbox input, and wherein the first and the second gearbox output are connected to the drive output device.
A hybrid drivetrain of said type is known from document WO 2012/079683 A2.
In the field of hybrid drivetrains, it is known for a drive unit in the form of an internal combustion engine to be assigned a further drive unit in the form of an electric machine. Here, the electric machine is generally of considerably lower power than the internal combustion engine. In some embodiments, the electric machine can provide drive power for purely electric driving, wherein purely electric driving operation is restricted owing to the electrical energy store that must be provided. A compromise must generally be found here, because a large electrical energy store leads to a high vehicle weight. A small electrical energy store leads to a short electric travelling range. In many cases, the electric travelling range is only a few kilometres. The electric machine can however also be used for other operating modes, for example for a boost mode, for the starting of the internal combustion engine, or for the charging of the electrical energy store (in a recuperation operating mode).
Such hybrid drive concepts do not fully exploit the possibilities of electric machines as a drive. This is because electric machines have the advantage, as a drive motor, that they can provide a high torque even at low rotational speeds, and in many operating modes exhibit greater efficiency than the internal combustion engine.
Furthermore, in the field of hybrid drivetrains, so-called “range extender concepts” are known. The basic idea of said concepts consists in at least predominantly using an electric machine for driving the motor vehicle. Furthermore, such concepts generally have a second electric machine which is designed for charging the electrical energy store and which is connected or connectable to the internal combustion engine. A typical operating state in the case of such range extender concepts consists in the internal combustion engine being kept in a rotational speed range that is expedient in terms of efficiency and hereby charging the electrical energy store by means of the second electric machine. In parallel with this, power from the electrical energy store is used for the first electric machine, which drives the vehicle. In some embodiments, the internal combustion engine may in this case be used to assist in providing drive, though this increases the complexity of such range extender concepts.
Known range extender concepts also have a gearbox arrangement. Here, it is for example known for the gearbox to be equipped with a single fixed transmission ratio. Since the electric machine that acts as a drive motor can operate over a large rotational speed range, a gearbox arrangement of said type may be adequate. In other gearbox arrangements, multiple gear stages may be provided. It is for example known for the gearbox arrangement to be in the form of a powershift-capable two-gear gearbox.
A disadvantage of some range extender concepts is that, in the case of a driving profile in which the vehicle is driven initially in an urban area, then over a relatively long distance, and then in the urban area again, purely electric driving is initially possible with the battery in the urban area, but then the battery is discharged relatively quickly during electric driving over the relatively long distance, such that a switch must be made to internal combustion engine operation. In this case, purely electric driving is then no longer possible in the urban traffic at the destination, because the battery has been discharged.
Furthermore, many hybrid drive concepts are afflicted by the fact that the acceleration by means of the internal combustion engine and the recuperation by means of the electric machine entail a very poor efficiency chain.
Furthermore, in many hybrid drivetrain concepts, provision is made for the electric machine to be used over as broad an operating range as possible. This then consequently often leads to large battery sizes; this in turn leads to a high weight, with the consequential result of low acceleration capability of the motor vehicle, specifically in the lower speed range.
The document WO 2012/079683 A2 mentioned in the introduction discloses a hybrid drivetrain which has a single electric machine and a single internal combustion engine. The drive device of the electric machine is connected to a gearbox output via a two-gear gearbox. The internal combustion engine is connected to a gearbox output via a three-gear gearbox, wherein the gearbox outputs are formed by a common output shaft which is connected to a differential. In the case of said drive concept, the two gearbox arrangements can be shifted independently of one another, and the rotational speeds of the internal combustion engine and of the electric machine can be selected independently of one another within the scope of the available gears.
It is also provided that the peak power of the electric motor amounts to at least 30%, in particular at least 100% of the rated power of the internal combustion engine. It is considered to be particularly preferable for the continuous power output of the electric motor to amount to approximately 80% of the rated power of the internal combustion engine or higher.
The intention of this is to make it possible to realize a fully-fledged driving function with the electric motor. In particular, it is provided here that the three-stage gearbox arrangement which is connected to the internal combustion engine has a first gear stage in the form of a starting gear stage, a second gear stage in the form of a maximum speed gear stage, and a third gear stage as an efficiency gear stage. The two-gear gearbox arrangement which is connected to the electric machine is intended to have a first gear stage as a dynamic gear stage with short transmission ratio, and a second gear stage as a maximum speed gear stage.
In one variant, provision is made for the output shaft of the electric machine and the output shaft of the internal combustion engine to be connected to one another by means of an intermediate shaft in order to permit standstill charging. In a third variant, provision is made for a first gear stage, which is configured as a starting and low gear, of the internal combustion engine to be realized through joint use of the sub-gearbox provided for the electric motor.